1. Field of the Invention
The present invention relates to a method of removing residual particles, and particularly to a method of removing residual contaminants in grooves of an alignment mark of a semiconductor wafer after a chemical-mechanical polishing.
2. Description of the Prior Art
The handling during semiconductor fabricating processes, such as cutting, lapping, polishing, or packaging, generally results in large amounts of contamination, wherein much of the origin of the contamination is not well understood. The front part of fabricating very large scale integration (VLSI) circuits, such as forming gates or field oxides, generally requires stringent cleanness, wherein removal of the contaminants is usually done by rinsing in hot organic solvents, accompanied by ultrasonic agitation with power of about 1000 watt during wafer cleaning. However, the rear part of fabricating VLSI circuits, such as planarization or metallization, has a less stringent standard in cleaning. Unfortunately, some of the slurry used in a chemical-mechanical polishing (CMP) step remains over the wafer, especially in the grooves of alignment marks for lighography purpose. FIG. 1 shows a cross-sectional view of an alignment mark 10, wherein some particles 12 reside inside the grooves 14 of the alignment mark 10. These particles 12 disadvantageously make the positioning of photo masks during lithography step difficult. The residual particles 12 generated after CMP are conventionally removed by a scrubber apparatus. Unfortunately, only a portion of the particles 12 can be removed by the conventional method. Furthermore, even the cleaning procedure used in the front part of the fabrication can not apply to solve this problem due to, for example, the insuitability of the solvents for removing the particles inside the alignment marks, or due to the unwillingness of using those apparatus to remove the particles after CMP in being afraid of contaminating this apparatus by the rear part of the fabrication. There is, therefore, a need of inventing a procedure for removing residual slurry or particles in the alignment marks after CMP.